The present invention relates to programmable integrated electronic systems in general and concerns in particular such systems which are organised as an array of identical cells and intrinsically have a reprogramming capability when one or more of the cells constituting the said array are faulty.
In addition to integrated circuits of the "ASIC" (Application Specific Integrated Circuits), which are designed to fulfil a function specific to one application and require lengthy development time, and circuits of the "Gate Array" type, which consist or an array of logic gates and can be configured, by means of one or two interconnection masks, to meet a given specification, a new type of integrated circuit has appeared in recent years, known as the "FPGA" (Field-Programmable Gate Array). These "FPGA" circuits, a description of which can be found in the book published under the title "Field-Programmable Gate Arrays" by Kluwer Academic Publishers, are programmable logic systems which may have a high degree of complexity. They consist of a set of logic blocks and connecting components (programmable switches) enabling the said logic blocks to be assembled in a configuration which meets a given specification. To use such systems, it is necessary to construct, from the specification for the envisaged application, a logic diagram with predefined modules and to convert this logic diagram, by means of a suitable software tool, into a series of connections distributed within the silicon substrate and connecting the different logic blocks so as to enable the system to function in accordance with the specification. Although having a higher performance than "Gate Arrays", since the logic blocks may carry out more complex functions, "FPGAs" nevertheless function in the same way as the former; that is to say, the cells are defined a priori and the program, which enables them to be interconnected and is defined from the specification of the application, is stored once and for all in the system memory or in the switches which define the function of the system. In these types of circuit there is no possibility of repair should one of the functional components fail.